An insulated conductor for a wire harness for a car, as shown in FIG. 1, comprises a bundle 2 of a plurality of insulated conductors 1 having a predetermined length with a covering 3 of tape wound on the bundle holding it together. Each of the insulated conductors 1 has ends exposed and parts 7 such as connectors connected to the exposed ends.
Lately, there have been various specifications of a car, which increases the number of parts and the number of wiring circuits. Accordingly, a wire harness has the diameter enlarged and the weight increased. For example, the diameter of the wire harness for the car changes from 20 through 30 mm of the prior art harness to 50 through 60 mm. It will be noted that this is contrary to the requirement of enlargement of a space within the car and of lightness of the car. Also, this causes the weight of the wire harness to increase and the number of operators for assembling the wire harness to increase. Thus, it will be noted that the smaller diameter and lighter weight of the wire harness are required for meeting the requirement of car design and for assembling the wire harness without any decrease in effectiveness of operation.
As shown in FIG. 2, one of the prior art insulated conductors for wire harness comprises an insulation 5 of vinyl chloride provided on a conductor 4. The conductor 4 comprises a twisted conductor formed by twisting a plurality of copper wire elements 4a while the insulation 5 is formed by extruding vinyl chloride on the twisted conductor. The thickness of the insulation 5 normally ranges from 0.6 mm to 1.1 mm and is 0.4 mm in case of thinnest insulation.
In order to make the diameter of the wire harness smaller, it is effective to thin the insulation 5 of the insulated conductor. However, if the insulation 5 is thinned, the abrasion resistance of the insulated conductor is lowered, which disadvantageously causes the insulation of the insulated conductor to be damaged when the wire harness is assembled, installed and treated thereafter.
The conductor 4 of twisted wires provides flexibility and softness to the insulated conductor, which preferably aids the conductor to be compressively secured to terminals, but the twisted conductor tends to have wire elements untwisted and protruded, which causes the cross section of the insulation on the conductor to have an out-of-round excursion as indicated by dotted line of FIG. 2 with the result that the insulation 5 of vinyl chloride tends to have a thick portion as indicated by t (max) and a thin portion as indicated by t (min). In case that terminals are compressively secured to the ends of the insulated conductor, the insulation at the ends of the insulated conductor has to be removed. This is accomplished by stripping blades 6 into the insulation 5, as shown in FIG. 3, so that the blades 6 never contact the conductor 4 while they are moved as indicated by an arrow in FIG. 3. If the blades 6 contact the conductor by any chance, then the conductor 4 is damaged, which causes the insulated condcutor to be cut due to vibration applied thereto from the car. If the insulation 5 is thicker, the conductor 4 is never damaged even though the wire elements 4a are slightly untwisted or protruded, but if the insulation is thinner and the wire elements 4a are untwisted or protruded, this causes the conductor 4 to be possibly damaged when the insulation is removed.